1. Field of the Invention
The present invention relates to nautical systems for the detection and location of man overboard and related conditions including, inboard monitoring, overboard monitoring and combined monitoring. More specifically, the present invention relates to the monitoring of a vessel's personnel, crew, passengers and/or cargo with the ability to detect changes in monitored conditions and to provide an indication of the time of any change and the location of the vessel at the time of the change in monitored condition.
2. Description of Prior Art
A man overboard condition can include the loss of a vessel's personnel, crew, passengers and/or cargo. A significant danger in traveling by water is the loss of life and property due to the loss of persons or articles which fall overboard from a vessel. It is not uncommon, especially on large vessels, for a man-overboard to remain unnoticed for a significant period of time. The likelihood of successful rescue decreases significantly if a man-overboard is not located soon after entering the water. The length of time and urgency of rescue is affected by many factors, including sea temperature, predator infestation and weather.
Several devices have been proposed to aid in detection of a man-overboard, including the personal ocean security system of U.S. Pat. No. 4,549,169 which teaches transmitters operating within a narrow frequency band so as to assure suppression of the transmission when submerged. Each transmitter continually transmits to a monitoring station, or, in one embodiment, responds to an encoded interrogation signal from the monitoring station. When a person falls overboard, the transmitter is submerged, and thus the monitoring station receives no more signals from it, thereby indicating that the person is in the water.
The safety alert and locating system of U.S. Pat. No. 4,813,025 combines detection and location by a combination of interrogation and response signals transmitted through both air and water, received by spaced antenna on the vessel to measure both elapsed time and incoming phase angles to determine distance and angle. The system automatically determines when a person under safety surveillance has exceeded safety limits from a base location.
The apparatus of U.S. Pat. No. 3,588,858 includes a radio transmitter actuated by a position sensitive switch, to create an alert or alarm situation when a person is in an abnormal position. The system of U.S. Pat. No. 4,305,143 includes an ultrasonic transmitter actuated by a hydrostatic switch, to send ultrasonic signals through die water to a receiver on the boat.
In U.S. Pat. No. 4,442,426 a monitoring system is shown in which a plurality of remote transmitter stations send signals to a central monitor in time staggered sequence. Each signal may be coded to identify the remote transmitter. When a danger situation arises, an alarm signal is sent without delay, breaking into the sequential pattern and thus informing the central monitor of an alarm condition.
Several devices have also been proposed to aid in location of a man-overboard, including U.S. Pat. No. 5,408,238 which teaches an apparatus with a GPS receiver which rebroadcasts its GPS coordinates to provide location information. The device is not attached to an individual nor automatically deployed. It is large and must be manually tossed into the water after an emergency condition is identified.
U.S. Pat. No. 5,274,359 teaches a portable water activated alert system with directional indicator which utilizes a directional antenna to receive a signal from a water activated transmitter to guide the vessel back toward the overboard transmitter.
There are also a number of patents which teach various water activated switches, for example U.S. Pat. No. 4,068,221, immersion responsive sensor and U.S. Pat. No. 5,408,222 submersion warning device and U.S. Pat. No. 5,138,300 water immersion alarm system.
In all of the foregoing prior art patents, an alarm or danger condition is indicated when it occurs, and, in some instances, the central station is capable of taking some sort of rescue or danger alleviating action. None of the patents shows a system capable of recording an exact time and location of the incident for rapid and effective rescue. Any of the systems which do provide location information do so as a location relative to the vessel and rely upon continued reception of a signal from the individual transmitter to maintain that location information, however, continued transmission can be unreliable when the vessel is traveling away from the lost individual.